Hi Gang,
I have an old Oak Hills Research Classic 40/20 meter xcvr. I'm not sure
if this is a new problem or something that has always plagued it, but I am
getting several spurious signals on both 40 and 20. I have identified one
of them as a local AMBC station at 1500KHz. After reviewing the schematic,
it looks like the trouble could be in one of several areas. This unit
makes wide use of diode switching for the Tx and Rx paths, and I'm
suspecting the 50KW BC station is driving one of more of them into
conduction.
The other possible culprit I see is that this rig has an untuned
broadband BJT amp right after the LPF. This circuit is obviously biased at
a fairly high level of current which I'm sure was intended to make it
robust in the presence of strong signals, but I'm thinking it may not be
able to handle all the RF it is seeing.
Before I tear into the rig and try some things, bypassing diode switching
and/or adding a preselector to that RF amp, I wanted to check with you guys
and see if someone has already 'invented this wheel'.

Tnx!

Bob WB0POQ